/*
 * jdhuff.c
 *
 * Copyright (C) 1991-1995, Thomas G. Lane.
 * This file is part of the Independent JPEG Group's software.
 * For conditions of distribution and use, see the accompanying README file.
 *
 * This file contains Huffman entropy decoding routines.
 *
 * Much of the complexity here has to do with supporting input suspension.
 * If the data source module demands suspension, we want to be able to back
 * up to the start of the current MCU.  To do this, we copy state variables
 * into local working storage, and update them back to the permanent
 * storage only upon successful completion of an MCU.
 */

#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"
#include "jdhuff.h"      /* Declarations shared with jdphuff.c */


/*
 * Expanded entropy decoder object for Huffman decoding.
 *
 * The savable_state subrecord contains fields that change within an MCU,
 * but must not be updated permanently until we complete the MCU.
 */

typedef struct {
    int last_dc_val[MAX_COMPS_IN_SCAN];/* last DC coef for each component */
} savable_state;

/* This macro is to work around compilers with missing or broken
 * structure assignment.  You'll need to fix this code if you have
 * such a compiler and you change MAX_COMPS_IN_SCAN.
 */

#ifndef NO_STRUCT_ASSIGN
#define ASSIGN_STATE( dest, src )  ( ( dest ) = ( src ) )
#else
#if MAX_COMPS_IN_SCAN == 4
#define ASSIGN_STATE( dest, src )  \
    ( ( dest ).last_dc_val[0] = ( src ).last_dc_val[0], \
     ( dest ).last_dc_val[1] = ( src ).last_dc_val[1], \
     ( dest ).last_dc_val[2] = ( src ).last_dc_val[2], \
     ( dest ).last_dc_val[3] = ( src ).last_dc_val[3] )
#endif
#endif


typedef struct {
    struct jpeg_entropy_decoder pub;/* public fields */

    /* These fields are loaded into local variables at start of each MCU.
     * In case of suspension, we exit WITHOUT updating them.
     */
    bitread_perm_state bitstate;/* Bit buffer at start of MCU */
    savable_state      saved; /* Other state at start of MCU */

    /* These fields are NOT loaded into local working state. */
    unsigned int restarts_to_go;/* MCUs left in this restart interval */

    /* Pointers to derived tables (these workspaces have image lifespan) */
    d_derived_tbl * dc_derived_tbls[NUM_HUFF_TBLS];
    d_derived_tbl * ac_derived_tbls[NUM_HUFF_TBLS];
} huff_entropy_decoder;

typedef huff_entropy_decoder * huff_entropy_ptr;


/*
 * Initialize for a Huffman-compressed scan.
 */

METHODDEF void
start_pass_huff_decoder( j_decompress_ptr cinfo ) {
    huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
    int ci, dctbl, actbl;
    jpeg_component_info * compptr;

    /* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG.
     * This ought to be an error condition, but we make it a warning because
     * there are some baseline files out there with all zeroes in these bytes.
     */
    if ( ( cinfo->Ss != 0 ) || ( cinfo->Se != DCTSIZE2 - 1 ) ||
        ( cinfo->Ah != 0 ) || ( cinfo->Al != 0 ) ) {
        WARNMS( cinfo, JWRN_NOT_SEQUENTIAL );
    }

    for ( ci = 0; ci < cinfo->comps_in_scan; ci++ ) {
        compptr = cinfo->cur_comp_info[ci];
        dctbl = compptr->dc_tbl_no;
        actbl = compptr->ac_tbl_no;
        /* Make sure requested tables are present */
        if ( ( dctbl < 0 ) || ( dctbl >= NUM_HUFF_TBLS ) ||
            ( cinfo->dc_huff_tbl_ptrs[dctbl] == NULL ) ) {
            ERREXIT1( cinfo, JERR_NO_HUFF_TABLE, dctbl );
        }
        if ( ( actbl < 0 ) || ( actbl >= NUM_HUFF_TBLS ) ||
            ( cinfo->ac_huff_tbl_ptrs[actbl] == NULL ) ) {
            ERREXIT1( cinfo, JERR_NO_HUFF_TABLE, actbl );
        }
        /* Compute derived values for Huffman tables */
        /* We may do this more than once for a table, but it's not expensive */
        jpeg_make_d_derived_tbl( cinfo, cinfo->dc_huff_tbl_ptrs[dctbl],
                                 &entropy->dc_derived_tbls[dctbl] );
        jpeg_make_d_derived_tbl( cinfo, cinfo->ac_huff_tbl_ptrs[actbl],
                                 &entropy->ac_derived_tbls[actbl] );
        /* Initialize DC predictions to 0 */
        entropy->saved.last_dc_val[ci] = 0;
    }

    /* Initialize bitread state variables */
    entropy->bitstate.bits_left = 0;
    entropy->bitstate.get_buffer = 0;/* unnecessary, but keeps Purify quiet */
    entropy->bitstate.printed_eod = FALSE;

    /* Initialize restart counter */
    entropy->restarts_to_go = cinfo->restart_interval;
}


/*
 * Compute the derived values for a Huffman table.
 * Note this is also used by jdphuff.c.
 */

GLOBAL void
jpeg_make_d_derived_tbl( j_decompress_ptr cinfo, JHUFF_TBL * htbl,
                         d_derived_tbl ** pdtbl ) {
    d_derived_tbl * dtbl;
    int p, i, l, si;
    int lookbits, ctr;
    char huffsize[257];
    unsigned int huffcode[257];
    unsigned int code;

    /* Allocate a workspace if we haven't already done so. */
    if ( *pdtbl == NULL ) {
        *pdtbl = (d_derived_tbl *)
                 ( *cinfo->mem->alloc_small )( (j_common_ptr) cinfo, JPOOL_IMAGE,
                                              SIZEOF( d_derived_tbl ) );
    }
    dtbl = *pdtbl;
    dtbl->pub = htbl;   /* fill in back link */

    /* Figure C.1: make table of Huffman code length for each symbol */
    /* Note that this is in code-length order. */

    p = 0;
    for ( l = 1; l <= 16; l++ ) {
        for ( i = 1; i <= (int) htbl->bits[l]; i++ ) {
            huffsize[p++] = (char) l;
        }
    }
    huffsize[p] = 0;

    /* Figure C.2: generate the codes themselves */
    /* Note that this is in code-length order. */

    code = 0;
    si = huffsize[0];
    p = 0;
    while ( huffsize[p] ) {
        while ( ( (int) huffsize[p] ) == si ) {
            huffcode[p++] = code;
            code++;
        }
        code <<= 1;
        si++;
    }

    /* Figure F.15: generate decoding tables for bit-sequential decoding */

    p = 0;
    for ( l = 1; l <= 16; l++ ) {
        if ( htbl->bits[l] ) {
            dtbl->valptr[l] = p;/* huffval[] index of 1st symbol of code length l */
            dtbl->mincode[l] = huffcode[p];/* minimum code of length l */
            p += htbl->bits[l];
            dtbl->maxcode[l] = huffcode[p - 1];/* maximum code of length l */
        } else {
            dtbl->maxcode[l] = -1;/* -1 if no codes of this length */
        }
    }
    dtbl->maxcode[17] = 0xFFFFFL;/* ensures jpeg_huff_decode terminates */

    /* Compute lookahead tables to speed up decoding.
     * First we set all the table entries to 0, indicating "too long";
     * then we iterate through the Huffman codes that are short enough and
     * fill in all the entries that correspond to bit sequences starting
     * with that code.
     */

    MEMZERO( dtbl->look_nbits, SIZEOF( dtbl->look_nbits ) );

    p = 0;
    for ( l = 1; l <= HUFF_LOOKAHEAD; l++ ) {
        for ( i = 1; i <= (int) htbl->bits[l]; i++, p++ ) {
            /* l = current code's length, p = its index in huffcode[] & huffval[]. */
            /* Generate left-justified code followed by all possible bit sequences */
            lookbits = huffcode[p] << ( HUFF_LOOKAHEAD - l );
            for ( ctr = 1 << ( HUFF_LOOKAHEAD - l ); ctr > 0; ctr-- ) {
                dtbl->look_nbits[lookbits] = l;
                dtbl->look_sym[lookbits] = htbl->huffval[p];
                lookbits++;
            }
        }
    }
}


/*
 * Out-of-line code for bit fetching (shared with jdphuff.c).
 * See jdhuff.h for info about usage.
 * Note: current values of get_buffer and bits_left are passed as parameters,
 * but are returned in the corresponding fields of the state struct.
 *
 * On most machines MIN_GET_BITS should be 25 to allow the full 32-bit width
 * of get_buffer to be used.  (On machines with wider words, an even larger
 * buffer could be used.)  However, on some machines 32-bit shifts are
 * quite slow and take time proportional to the number of places shifted.
 * (This is true with most PC compilers, for instance.)  In this case it may
 * be a win to set MIN_GET_BITS to the minimum value of 15.  This reduces the
 * average shift distance at the cost of more calls to jpeg_fill_bit_buffer.
 */

#ifdef SLOW_SHIFT_32
#define MIN_GET_BITS  15    /* minimum allowable value */
#else
#define MIN_GET_BITS  ( BIT_BUF_SIZE - 7 )
#endif


GLOBAL boolean
jpeg_fill_bit_buffer( bitread_working_state * state,
                      register bit_buf_type get_buffer, register int bits_left,
                      int nbits ) {
/* Load up the bit buffer to a depth of at least nbits */
/* Copy heavily used state fields into locals (hopefully registers) */
    register const JOCTET * next_input_byte = state->next_input_byte;
    register size_t bytes_in_buffer = state->bytes_in_buffer;
    register int c;

    /* Attempt to load at least MIN_GET_BITS bits into get_buffer. */
    /* (It is assumed that no request will be for more than that many bits.) */

    while ( bits_left < MIN_GET_BITS ) {
        /* Attempt to read a byte */
        if ( state->unread_marker != 0 ) {
            goto no_more_data;
        }                   /* can't advance past a marker */

        if ( bytes_in_buffer == 0 ) {
            if ( !( *state->cinfo->src->fill_input_buffer )( state->cinfo ) ) {
                return FALSE;
            }
            next_input_byte = state->cinfo->src->next_input_byte;
            bytes_in_buffer = state->cinfo->src->bytes_in_buffer;
        }
        bytes_in_buffer--;
        c = GETJOCTET( *next_input_byte++ );

        /* If it's 0xFF, check and discard stuffed zero byte */
        if ( c == 0xFF ) {
            do {
                if ( bytes_in_buffer == 0 ) {
                    if ( !( *state->cinfo->src->fill_input_buffer )( state->cinfo ) ) {
                        return FALSE;
                    }
                    next_input_byte = state->cinfo->src->next_input_byte;
                    bytes_in_buffer = state->cinfo->src->bytes_in_buffer;
                }
                bytes_in_buffer--;
                c = GETJOCTET( *next_input_byte++ );
            } while ( c == 0xFF );

            if ( c == 0 ) {
                /* Found FF/00, which represents an FF data byte */
                c = 0xFF;
            } else {
                /* Oops, it's actually a marker indicating end of compressed data. */
                /* Better put it back for use later */
                state->unread_marker = c;

no_more_data:
                /* There should be enough bits still left in the data segment; */
                /* if so, just break out of the outer while loop. */
                if ( bits_left >= nbits ) {
                    break;
                }
                /* Uh-oh.  Report corrupted data to user and stuff zeroes into
                 * the data stream, so that we can produce some kind of image.
                 * Note that this code will be repeated for each byte demanded
                 * for the rest of the segment.  We use a nonvolatile flag to ensure
                 * that only one warning message appears.
                 */
                if ( ! * ( state->printed_eod_ptr ) ) {
                    WARNMS( state->cinfo, JWRN_HIT_MARKER );
                    *( state->printed_eod_ptr ) = TRUE;
                }
                c = 0;/* insert a zero byte into bit buffer */
            }
        }

        /* OK, load c into get_buffer */
        get_buffer = ( get_buffer << 8 ) | c;
        bits_left += 8;
    }

    /* Unload the local registers */
    state->next_input_byte = next_input_byte;
    state->bytes_in_buffer = bytes_in_buffer;
    state->get_buffer = get_buffer;
    state->bits_left = bits_left;

    return TRUE;
}


/*
 * Out-of-line code for Huffman code decoding.
 * See jdhuff.h for info about usage.
 */

GLOBAL int
jpeg_huff_decode( bitread_working_state * state,
                  register bit_buf_type get_buffer, register int bits_left,
                  d_derived_tbl * htbl, int min_bits ) {
    register int l = min_bits;
    register INT32 code;

    /* HUFF_DECODE has determined that the code is at least min_bits */
    /* bits long, so fetch that many bits in one swoop. */

    CHECK_BIT_BUFFER( *state, l, return -1 );
    code = GET_BITS( l );

    /* Collect the rest of the Huffman code one bit at a time. */
    /* This is per Figure F.16 in the JPEG spec. */

    while ( code > htbl->maxcode[l] ) {
        code <<= 1;

        CHECK_BIT_BUFFER( *state, 1, return -1 );
        code |= GET_BITS( 1 );
        l++;
    }

    /* Unload the local registers */
    state->get_buffer = get_buffer;
    state->bits_left = bits_left;

    /* With garbage input we may reach the sentinel value l = 17. */

    if ( l > 16 ) {
        WARNMS( state->cinfo, JWRN_HUFF_BAD_CODE );
        return 0;       /* fake a zero as the safest result */
    }

    return htbl->pub->huffval[ htbl->valptr[l] +
                               ( (int) ( code - htbl->mincode[l] ) ) ];
}


/*
 * Figure F.12: extend sign bit.
 * On some machines, a shift and add will be faster than a table lookup.
 */

#ifdef AVOID_TABLES

#define HUFF_EXTEND( x, s )  ( ( x ) < ( 1 << ( ( s ) - 1 ) ) ? ( x ) + ( ( ( -1 ) << ( s ) ) + 1 ) : ( x ) )

#else

#define HUFF_EXTEND( x, s )  ( ( x ) < extend_test[s] ? ( x ) + extend_offset[s] : ( x ) )

static const int extend_test[16] =   /* entry n is 2**(n-1) */
{ 0, 0x0001, 0x0002, 0x0004, 0x0008, 0x0010, 0x0020, 0x0040, 0x0080,
  0x0100, 0x0200, 0x0400, 0x0800, 0x1000, 0x2000, 0x4000 };

static const int extend_offset[16] = /* entry n is (-1 << n) + 1 */
{ 0, ( ( -1 ) << 1 ) + 1, ( ( -1 ) << 2 ) + 1, ( ( -1 ) << 3 ) + 1, ( ( -1 ) << 4 ) + 1,
  ( ( -1 ) << 5 ) + 1, ( ( -1 ) << 6 ) + 1, ( ( -1 ) << 7 ) + 1, ( ( -1 ) << 8 ) + 1,
  ( ( -1 ) << 9 ) + 1, ( ( -1 ) << 10 ) + 1, ( ( -1 ) << 11 ) + 1, ( ( -1 ) << 12 ) + 1,
  ( ( -1 ) << 13 ) + 1, ( ( -1 ) << 14 ) + 1, ( ( -1 ) << 15 ) + 1 };

#endif /* AVOID_TABLES */


/*
 * Check for a restart marker & resynchronize decoder.
 * Returns FALSE if must suspend.
 */

LOCAL boolean
process_restart( j_decompress_ptr cinfo ) {
    huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
    int ci;

    /* Throw away any unused bits remaining in bit buffer; */
    /* include any full bytes in next_marker's count of discarded bytes */
    cinfo->marker->discarded_bytes += entropy->bitstate.bits_left / 8;
    entropy->bitstate.bits_left = 0;

    /* Advance past the RSTn marker */
    if ( !( *cinfo->marker->read_restart_marker )( cinfo ) ) {
        return FALSE;
    }

    /* Re-initialize DC predictions to 0 */
    for ( ci = 0; ci < cinfo->comps_in_scan; ci++ ) {
        entropy->saved.last_dc_val[ci] = 0;
    }

    /* Reset restart counter */
    entropy->restarts_to_go = cinfo->restart_interval;

    /* Next segment can get another out-of-data warning */
    entropy->bitstate.printed_eod = FALSE;

    return TRUE;
}


/*
 * Decode and return one MCU's worth of Huffman-compressed coefficients.
 * The coefficients are reordered from zigzag order into natural array order,
 * but are not dequantized.
 *
 * The i'th block of the MCU is stored into the block pointed to by
 * MCU_data[i].  WE ASSUME THIS AREA HAS BEEN ZEROED BY THE CALLER.
 * (Wholesale zeroing is usually a little faster than retail...)
 *
 * Returns FALSE if data source requested suspension.  In that case no
 * changes have been made to permanent state.  (Exception: some output
 * coefficients may already have been assigned.  This is harmless for
 * this module, since we'll just re-assign them on the next call.)
 */

METHODDEF boolean
decode_mcu( j_decompress_ptr cinfo, JBLOCKROW * MCU_data ) {
    huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
    register int s, k, r;
    int blkn, ci;
    JBLOCKROW block;
    BITREAD_STATE_VARS;
    savable_state state;
    d_derived_tbl * dctbl;
    d_derived_tbl * actbl;
    jpeg_component_info * compptr;

    /* Process restart marker if needed; may have to suspend */
    if ( cinfo->restart_interval ) {
        if ( entropy->restarts_to_go == 0 ) {
            if ( !process_restart( cinfo ) ) {
                return FALSE;
            }
        }
    }

    /* Load up working state */
    BITREAD_LOAD_STATE( cinfo, entropy->bitstate );
    ASSIGN_STATE( state, entropy->saved );

    /* Outer loop handles each block in the MCU */

    for ( blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++ ) {
        block = MCU_data[blkn];
        ci = cinfo->MCU_membership[blkn];
        compptr = cinfo->cur_comp_info[ci];
        dctbl = entropy->dc_derived_tbls[compptr->dc_tbl_no];
        actbl = entropy->ac_derived_tbls[compptr->ac_tbl_no];

        /* Decode a single block's worth of coefficients */

        /* Section F.2.2.1: decode the DC coefficient difference */
        HUFF_DECODE( s, br_state, dctbl, return FALSE, label1 );
        if ( s ) {
            CHECK_BIT_BUFFER( br_state, s, return FALSE );

            r = GET_BITS( s );
            s = HUFF_EXTEND( r, s );
        }

        /* Shortcut if component's values are not interesting */
        if ( !compptr->component_needed ) {
            goto skip_ACs;
        }

        /* Convert DC difference to actual value, update last_dc_val */
        s += state.last_dc_val[ci];
        state.last_dc_val[ci] = s;
        /* Output the DC coefficient (assumes jpeg_natural_order[0] = 0) */
        ( *block )[0] = (JCOEF) s;

        /* Do we need to decode the AC coefficients for this component? */
        if ( compptr->DCT_scaled_size > 1 ) {

            /* Section F.2.2.2: decode the AC coefficients */
            /* Since zeroes are skipped, output area must be cleared beforehand */
            for ( k = 1; k < DCTSIZE2; k++ ) {
                HUFF_DECODE( s, br_state, actbl, return FALSE, label2 );

                r = s >> 4;
                s &= 15;

                if ( s ) {
                    k += r;

                    CHECK_BIT_BUFFER( br_state, s, return FALSE );
                    r = GET_BITS( s );
                    s = HUFF_EXTEND( r, s );
                    /* Output coefficient in natural (dezigzagged) order.
                     * Note: the extra entries in jpeg_natural_order[] will save us
                     * if k >= DCTSIZE2, which could happen if the data is corrupted.
                     */
                    ( *block )[jpeg_natural_order[k]] = (JCOEF) s;
                } else {
                    if ( r != 15 ) {
                        break;
                    }
                    k += 15;
                }
            }

        } else {
skip_ACs:

            /* Section F.2.2.2: decode the AC coefficients */
            /* In this path we just discard the values */
            for ( k = 1; k < DCTSIZE2; k++ ) {
                HUFF_DECODE( s, br_state, actbl, return FALSE, label3 );

                r = s >> 4;
                s &= 15;

                if ( s ) {
                    k += r;

                    CHECK_BIT_BUFFER( br_state, s, return FALSE );
                    DROP_BITS( s );
                } else {
                    if ( r != 15 ) {
                        break;
                    }
                    k += 15;
                }
            }

        }
    }

    /* Completed MCU, so update state */
    BITREAD_SAVE_STATE( cinfo, entropy->bitstate );
    ASSIGN_STATE( entropy->saved, state );

    /* Account for restart interval (no-op if not using restarts) */
    entropy->restarts_to_go--;

    return TRUE;
}


/*
 * Module initialization routine for Huffman entropy decoding.
 */

GLOBAL void
jinit_huff_decoder( j_decompress_ptr cinfo ) {
    huff_entropy_ptr entropy;
    int i;

    entropy = (huff_entropy_ptr)
              ( *cinfo->mem->alloc_small )( (j_common_ptr) cinfo, JPOOL_IMAGE,
                                           SIZEOF( huff_entropy_decoder ) );
    cinfo->entropy = (struct jpeg_entropy_decoder *) entropy;
    entropy->pub.start_pass = start_pass_huff_decoder;
    entropy->pub.decode_mcu = decode_mcu;

    /* Mark tables unallocated */
    for ( i = 0; i < NUM_HUFF_TBLS; i++ ) {
        entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL;
    }
}
